The disclosure relates to pipettors of the type which are capable of picking up and ejecting an accurate volume of a liquid. Glass pipettes have been used for many years to draw up an accurate volume of liquid and eject it into a desired vessel. Typically, each pipette was graduated to draw up and measure a single volume of liquid. The volume of the liquid was determined typically by a graduated mark on the pipettor, and a certain amount of skill and care was required to obtain an accurate volume. Later, volumetric pipettors were developed which are capable of drawing in a particular volume of liquid by simply depressing and releasing a button located on the end of the pipettor. Further improvements were made by provision of means for adjusting a pipettor to eject varying volumes depending upon a setting on the adjustable pipettor.
Although volumetric pipettors and variable pipettors greatly facilitate the measurement of small volumes of liquid, they are both expensive and are capable of being incorrectly set or used. An inexpensive and essentially fool-proof device is needed to enable the rapid, accurate measurement volumes of liquid.